Apparatus for the treatment of water by injection of ozone and carbon dioxide

ABSTRACT

A process and device for treatment of water circulating in a conduit, which water carries microorganisms that must be eliminated and ions susceptible of leading to the formation of deposits on the internal wall of the conduit. To this end, there is injected in the water to be treated effective quantities of ozone and carbon dioxide. Particularly useful to treat the water conduits of a hospital building.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of application Ser. No. 09/137,238, filedAug. 20, 1998 now U.S. Pat. No. 6,096,221.

FIELD OF THE INVENTION

The present invention relates to a process and device for the treatmentof water flowing in a conduit, which water carries microorganisms thatmust be eliminated and ions adapted to lead to formation of deposits onthe internal wall of said conduit.

BACKGROUND OF THE INVENTION

It is known to subject the water flowing in a conduit or a network ofconduits, to treatment adapted to disinfect it, which is to say toeliminate the microorganisms which it carries.

To this end, a first solution consists in introducing into the waterchemical agents, such as chlorine or chlorine derivatives. However, thistype of chemical agent has several drawbacks.

Thus, once introduced into the water, the latter lead to the formationof biproducts of chlorination, such as organo-chlorine products, whichare undesirable substances, whose accumulation in the conduits carryingthe water for human consumption, is likely to give rise to problems ofpublic health.

Moreover, it has been noted that chlorine gives rise to internalcorrosion of the conduits of the network, thus creating cavities in thewalls of the conduits which promote the deposit, growth and propagationof a biofilm of microorganisms.

Moreover, it has been noted that certain pathogenic germs resist theaction of chlorine and its derivatives.

An alternative to the use of chlorine derivatives is the use of ozone oran ozonated gas injected directly into the water to be treated.

Thus, the fact of sending ozone into a conduit colonized by bacterialimits the development of these latter and improves the quality of thewater. In other words, the ozone permits reducing the living bacterialflora carried by the water to a threshold below the detectable limit.These variable doses used do not give rise to the formation ofbiodegradable dissolved organic carbon (BDOC), which serves to nourishthe bacterial flora; the risks of revival of the microorganisms arehence reduced.

Moreover, the breakdown of the ozone does not lead to subproductsadapted to harm public health and does not give rise moreover to anyproblem of corrosion of the pipes.

Another problem to which it is necessary to give attention, is that ofthe progressive deposits on the internal wall of the pipes by deposit onthe latter of ions carried by the water. This deposit is greater whenthe conveyed water is warm because the temperature favors shifting thecalco-carbon equilibrium, leading to calcarious deposits.

Such ionic deposits leading to the formation of scale in the pipes areundesirable because on the one hand they give rise to progressiveclogging of the pipes and on the other hand they favor and facilitatethe implantation and growth of a biofilm of microorganisms.

To limit these scaling phenomena, it is necessary to bring the water tocalco-carbonic equilibrium, which is effected in a known manner byeither restoring the equilibrium of the water with salt, or, as the casemay be, changing the pH.

Conventionally, the re-equilibrating water with salt requires a complexand costly material, whose principal operation is based on ion exchangetechnique, whilst requiring the use of a large quantity of reagent. Ifthis technique permits solving at least partially the problem of scalingin pipes, it also gives rise to untimely development of microorganisms.

Changing the pH, and hence the calco-carbonic equilibrium toward acidpH, can be carried out itself by introduction into the water to betreated of strong acids, such as 97% sulfuric acid or 35% hydrochloricacid, or a weak acid. However, the use of acid products gives rise toseveral drawbacks, namely, their handling is difficult and potentiallydanger for the user, the acids are a source of pollutant ions for thewater (SO₄ ²⁻, Cl⁻ ions . . . ), the acidity is a cause of corrosion ofpipes, the doses added to the water must be very carefully controlled soas to avoid any risk of over or under acidification of the water.

An alternative to the use of acids or salts consists in the dissolutionin the water to be treated of carbon dioxide (CO₂), which permitsreducing the pH of the water effectively, easily and stably.

Moreover, when it is desired to treat water flowing in a pipe, whichwater carries microorganisms and ions promoting scaling in the pipe, itis recommended to inject ozone (O₃) therein, and carbon dioxide (CO₂).Thus, in this way, there is a synergetic action of the two gases.

More particularly, the ozone will permit eliminating the microorganismscarried by the water and the CO₂ will prevent or slow the formation ofscale and hence the deposit of the biofilm of microorganisms on theinternal walls of the pipes.

The injection of ozone and carbon dioxide into water to be treated canbe carried out either by injecting these two gases independently of eachother, or by using a preliminary mixing of them, thus we will speak ofsimultaneous injection of the two gases.

The field of application of this type of water treatment process is verywide and relates particularly to the hospital field (fighting nosocomialinfections due to Legionelle, Pseudomonas . . . ), or generally: theprotection of piping against clogging due to scaling and to the depositof biofilm on their internal walls, and the industrial sector: treatmentof water for subsequent processes, combatting clogging of piping andheat exchangers . . . .

Until now, numerous processes disclosing treatment of water with ozonegas and/or carbon dioxide have been described and there can be cited orexample EP-A-0 567 860, WO95/13989, U.S. Pat. No. 5,085,809, JP-A-0490891.

SUMMARY OF THE INVENTION

The object of the present invention is to improve the existing processesso as to permit effective and optimum treatment of water.

Moreover particularly, the object of the invention is a process based onan injection of carbon dioxide (CO₂) and ozone (O₃) in variable andadjustable proportions as a function of the physico-chemical parametersof the water, such as pH, temperature and flow rate.

The invention thus relates to a process for the treatment of waterflowing in a conduit, which water carries microorganisms to beeliminated and ions adapted to lead to a formation of scale on theinternal wall of said conduit, in which:

a) at least the flow rate, temperature and inlet pH of the water to betreated are measured;

b) at least the outlet pH of the treated water is measured;

c) a reference pH is determined, from at least one of the parametersmeasured in step a);

d) the proportion of gas containing carbon dioxide to be injected intothe water to be treated is determined, by comparison of the reference pHdetermined in step c) and of the outlet pH measured in step b);

e) a reference value of ozonation is determined from at least one of theparameters measured in step a);

f) the proportion of gas containing ozone (O₃) to be injected into thewater to be treated is determined as a function of the reference valueof ozonation from step e);

g) the pH of the water is adjusted and at least a portion of themicroorganisms that it contains are eliminated, by injecting into thewater to be treated the proportion of gas containing ozone determined instep f) and the proportion of gas containing carbon dioxide determinedin step d).

As the case may be, the process of the invention can comprise one ormore of the following characteristics:

in step a), there is also measured at least one of the parameters of thegroup consisting of complete alkali-metric titer (CAT) and thehydrotimetric titer (HT);

in step b), there is also measured at least one of the parameters of thegroup consisting of residual ozone (RO₃), residual oxygen (RO₂) and theredox potential;

the reference value of ozonation is selected from the group consistingof the treatment rate (TR), the residual ozone (RO₃) and the productC×T;

the injection of gas in the water to be treated is carried out by meansof dissolution of the gases in water;

after injection of the gases into the water to be treated, at least aportion of the undissolved gas is eliminated by separation means for theundissolved gas;

the undissolved gases are eliminated by means of a vector gas,preferably a vector gas containing nitrogen;

after injection of the gases into the water to be treated, theundissolved gases are recovered;

in step c), the reference pH is determined at least from the temperatureand/or the inlet pH of the water to be treated;

in step d), the proportion of gas containing carbon dioxide to beinjected into the water to be treated is determined, thereby permittingreturning the outlet pH to a value substantially equal to the referencepH;

in step e), the reference value of ozonation is determined at least fromthe temperature and/or the flow rate of the water to be treated;

in step f), the proportion of ozone to be injected is determined alsofrom at least one of the parameters measured in step b) in the treatedwater;

the pressure of the water to be treated is maintained in the range of10⁵ Pa to 10⁶ Pa;

the injection of the gases into the water is carried out in line in aprincipal conduit or in a branch conduit connected to said principalconduit;

the injection of the gases is carried out in a continuous or sequentialmanner and preferably in a pipe in which the water to be treated flowswith a controlled flow rate;

the at least partial elimination of the microorganisms contained in thewater to be treated is carried out within a buffer reservoir locateddownstream of the injection site of the principal mixture;

the water to be treated is at a temperature below 100° C., preferablycomprised between 1° C. and 80° C.;

the pH of the water is adjusted to within the range 6 to 8.

The invention also relates to an installation for the treatment of waterflowing in a conduit (11, 11′), to practice the process described above,comprising:

a source of gas containing ozone,

a source of gas containing carbon dioxide,

means for dissolving in the water to be treated gas containing ozoneand/or gas containing carbon dioxide,

contact/homogenization means,

means for separating undissolved gases,

and measuring means.

Preferably, the means for separating undissolved gases are selected frompacked columns and centrifugal gas/liquid separators.

The process and/or installation described above is adapted to be used totreat water at a temperature from 1° C. to 80° C., flowing in a conduitin a building, preferably a hospital building, or in a conduit connectedto at least one heat exchanger.

The treatment rate (TR) is the quantity of ozone injected in the waterto be treated; it is expressed in grams of ozone injected per cubicmeter of effluent.

The residual ozone (RO₃) is the quantity of ozone dissolved in the waterto be treated; it is expressed in grams of ozone dissolved per cubicmeter of effluent and can be measured with a dissolved ozone probe or bychemical dosage.

The residual oxygen (RO₂) is the quantity of oxygen dissolved in thewater to be treated; it is expressed in grams of dissolved oxygen percubic meter of effluent and can be measured with a dissolved oxygenprobe.

The transfer yield (TY) is the quantity of gas actually transferred intothe water; it is expressed in percent and is given by the ratio:${TY} = \frac{\text{quantity of gas injected} - \text{quantity of gas discharged}}{\text{quantity of gas injected}}$

The product C×T defines the quantity of ozone which permits obtainingeffective elimination of the microorganisms, given that this eliminationdepends both on the concentration of dissolved ozone and on the time ofcontact between the ozonated water and the microorganisms to beeliminated as a function of the useful water volume of the reactor, inwhich this operation takes place. Thus, so as to ensure effectivetreatment of the water, the product C×T can be modified so as to takeaccount of the hydraulic behavior of the reactor or reactors, of thesuccessive stages of reagents. Moreover, according particularly to thenature and the number of the microorganisms, the nature of thedisinfectant used (here ozone) and of the quantity of water to betreated, the tables of values of C×T have been established by researchorganizations working on the treatment of water; there can be cited forexample the US EPA. The values of C×T given by these tables serve todimension the reactors; these latter are hence within the scope of aperson skilled in the art.

The calco-carbonic re-equilibriage is a chemical modification, which isto say a correction, of the water. Thus, there are found in water, as afunction of the pH and the degree of mineralization, more carbon dioxidein the form of free CO₂ or in the form of complexes Ca(HCO₃)₂ (calciumbicarbonate) and CaCO₃. It follows that when the water contains morefree CO₂, the latter is more corrosive for the pipes. Conversely, whenthe water contains more CO₂ in the form of complexes, the latter is moreapt to form scale in the pipes, in the form of accelerated precipitationof calcium carbonates in the form of scale. However, there remains anequilibrium pH for which the water is neither too corrosive nor toolikely to build up scale in the pipes. For example, to return a scaleforming water to an equilibrium pH, carbon dioxide can be injectedtherein so as to decrease the pH and hence thereby to minimize thepresence of CO₃ ²⁻ ions, which have a high tendency to react with thecations Ca²⁺ and Mg²⁺ giving scale, and to increase the presence of HCO₃⁻ ions which are non-reactive with said Ca²⁺ and Mg²⁺ cations.Thereupon, the complete alkalimetric titre (CAT) reflects the watercontent of OH⁻, CO₃ ²⁻ and HCO₃ ⁻, and the hydrotimetric titre (HT)gives the content of ions Ca²⁺ and Mg²⁺.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail with respect toembodiments given illustratively but non-limitatively, and shown in theaccompanying drawings, in which:

FIGS. 1-6 show six different embodiments of installations for practicingthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 shows a linear installation for the treatment of watercirculating in a conduit 11, with a substantially constant water flowrate, which water carries microorganisms to be eliminated and ionsadapted to form scale on the internal wall of said conduit; the waterhas been placed under positive pressure by compression means 6.

This installation comprises a source 1 of gas containing ozone (O₃),such as an ozonizer, supplied with oxygen by an oxygen source 1′, and asource 2 of carbon dioxide (CO₂). The source 1 of gas containing ozoneor ozonized gas is connected to dissolution means 3, for example agas/liquid emulsifier, arranged on conduit 11, which permit betterdissolution of the ozonized gas in the water. The dissolution means 3are for example a static mixer, a hydro-injector or a vacuum device ofthe venturi type.

Moreover, in this case, the injection of carbon dioxide gas (CO₂) in thewater is carried out directly in the principal conduit 11, downstream ofthe dissolution means 3.

As the case may be, the injection of gaseous carbon dioxide and ozonecan be controlled either by one and the same control module, such as aprogrammable computer, or by different modules (not shown). It is alsopossible to provide a remote overall surveillance and control mode forthe installation.

The water containing ozone and carbon dioxide then passes through thecontact/homogenization means 5, such as a contact reactor, in which thewater remains for the time necessary for effective action of the carbondioxide and ozone dissolved in the water to be treated, so as tore-establish the calco-carbonic equilibrium and to eliminate themicroorganisms likely to be found in it, then is directed to the phaseseparation means 4, such as a gas/liquid separator, permittingseparating the undissolved gases contained in the water carried by theconduit 11, namely essentially oxygen (O₂), from the carbon dioxide andresidual ozone.

After separation, these undissolved gases will be subjected to a thermalor catalytic treatment to eliminate from them residual ozone beforebeing discharged to the atmosphere by outlets (not shown), or arereusable in another treatment step, as well as the oxygen recoveredbeing adapted to be reused particularly for producing the ozone.

Separation means 4 of the phases are, for example, a tangential flowseparator or a reactor for separation of phases with control of thewater level and the pressure on the escape of undissolved gases.

After its passage through the separation means 4, the water is broughtto its utilization locality (not shown), by undergoing preferably a stepof chemical deozonization in deozonization means 8, for example byfiltration through active carbon, by use of a reactive reductor, such assodium bisulfite, or by desorption of the undissolved gases by“stripping”.

Measuring means 12, arranged upstream of the dissolution means 3, permitdetermining at the input the parameters indispensable to the goodoperation of the process of the invention: flow rate of water to betreated, temperature, inlet pH, the CAT and/or the HT. There are thendetermined from at least one of these parameters:

a reference pH, in general between 6 and 8; the parameters being thenpreferably the temperature and/or the inlet pH of the water to betreated;

and a reference ozonation value selected from the group comprised by thetreatment rate (TR), the residual ozone (RO₃) and the product C×T; theparameters then being preferably temperature and/or flow rate of waterto be treated, but also the outlet pH of the treated water, the residualozone (RO₃) and/or the residual oxygen (RO₂), which are determined atthe outlet downstream of the deozonization means 8, by second controlmeans 14.

By comparison of the reference pH and the measured outlet pH, theproportion of a gas containing carbon dioxide (CO₂) to be injected intothe water to be treated is determined, so as to obtain an outlet pHsubstantially equal to the reference pH.

Similarly, the proportion of gas containing ozone to be injected intothe water to be treated is determined as a function of the referenceozonation value. Then, the pH is adjusted thereby reestablishing thecalco-carbonic equilibrium of the water and at least a portion of themicroorganisms that it contains are eliminated, by injecting in thewater to be treated the effective proportions respectively of gascontaining ozone and gas containing carbon dioxide; the injection of gasbeing controlled and monitored by injection means 15 for gas.

A complementary control of the quantity of ozone dissolved is effectedupstream and/or downstream of the separation means 4 by first controlmeans 13.

Preferably, a central pilot module (not shown), such as a programmablecomputer, controls the whole of the installation: procedure and downtime or operating time, sequence of measurements, calculation of thetreatment standards . . . .

The installation shown in FIG. 1 can be used to treat warm water, whichis to say at a temperature between 1 and 100° C., carried by the conduitsystem of a hospital building.

The circulation of liquid and gaseous fluids with the installation andthe control of the pressure, could be carried out in a known manner withthe help of apparatus that is conventional for one skilled in the art,such as regulation valves, anti-return valves, pourers, expanders,pressure detectors, flow rate detectors . . . .

FIG. 2 shows an installation for the treatment of water analogous tothat shown in FIG. 1, except that the latter is no longer linear alongthe principal conduit 11, but is mounted branched from a branch conduit11′ (for common portions: compare FIG. 1); the water to be treatedflows, in this case, in the conduit 11 at a variable flow rate.

The derivative conduit 11′ removes at point A a portion of the waterflow circulating in the principal conduit 11, brings this water to betreated through dissolution means 3 arranged in the branch conduit 11′and the water flow rate thus ozonized is then returned to the conduit11, at point B. Compression means 6′ permit causing the water tocirculate in the branch conduit 11′.

According to this embodiment, the injection of CO₂ is carried out byinjection means 2 arranged downstream of the contact/homogenizationmeans 5; mixing means 7 are then arranged downstream of this injectionsite of the carbon dioxide in the water, but upstream of the phaseseparation means 4.

FIG. 3 shows an installation for the treatment of water analogous tothat shown in FIG. 2, except that the latter comprises, moreover, firstcontact/homogenization means 5′ and first phase separation means 4′arranged in the branch 11′ and downstream of the dissolution means 3;the first phase separation means 4′ being connected to thermaldestruction means 10′ of the undissolved ozone.

FIG. 4 shows an installation for the treatment of water analogous tothat shown in FIG. 3, except that, according to this embodiment, theozone and the carbon dioxide are injected into the water to be treated,via dissolution means 3, in the form of a gaseous mixture.

Moreover, subsidiary gas injection means 20, arranged upstream of themixing means 7, permit carrying out an injection into the water of avector gas, such as oxygen, nitrogen or air, which vector gas permitseliminating the undissolved gases (particularly ozone).

FIG. 5 shows an installation for treating water analogous to that shownin FIG. 1, except that, according to this embodiment, the deozonizationmeans 8 have been omitted. Moreover, the injection of carbon dioxidetakes place as in the embodiment of FIG. 2.

FIG. 6 shows an installation for the treatment of water analogous tothat shown in FIG. 5, except for the fact that, according to thisembodiment, the injection of carbon dioxide takes place according to theembodiment of FIG. 1 and that the subsidiary injection means 20 of gaspermit carrying out an injection into the water of a vector gas, asshown in FIG. 4.

What is claimed is:
 1. Apparatus for the treatment of water circulatingin a conduit, which water carries microorganisms to be eliminated andions likely to lead to formation of scale on the internal wall of saidconduit, the apparatus comprising: a) means for measuring at least theflow rate, the temperature and an inlet pH of the water to be treated;b) means for measuring at least an outlet pH of treated water; c) meansfor determining a reference pH from at least one of the parametersmeasured in a); d) means for determining by comparison of the referencepH determined in c) and of the outlet pH measured in b), the proportionof gas containing carbon dioxide (CO₂) to be injected into the water tobe treated; e) means for determining a reference ozonation value from atleast one of the parameters measured in a); f) means for determining, asa function of the reference ozonation value of e), the proportion of gascontaining ozone (O₃) to be injected into the water to be treated; andg) means for adjusting the pH of the water and means for eliminating atleast one portion of the microorganisms contained in said water, byinjecting into the water to be treated a gas containing the ozonedetermined in f) and the proportion of gas containing carbon dioxidedetermined in d).